Two weird fossils

Hot off the press are two new papers about fossil creatures, an insect and a “lobopod” that may be closely related to the ancestor of modern arthropods (insects, spiders, crustaceans, millipedes, etc.)

In the newest issue of Nature, Liu et al. (reference below) describe a fossil lobopod from the Chengjiang formation: a Chinese formation containing an amazing array of fossils from the early Cambrian (ca. 525-520 million years ago). Chengjiang has yielded many bizarre creatures—like the later Burgess Shale, it preserved many delicate animals—but this is one of the most striking. It’s a new lobopod, Diania cactiformis (note the species name: it really does look like a cactus):

The quality of preservation is amazing. What are lobopods? They are an early group of anomalous animals that bear a certain resemblance to the living onycophorans (“velvet worms”), once thought to be a “missing link” between annelid worms and arthropods. Lobopods have often been seen as a stem group of modern arthopods: a stem group is an extinct group that is more closely related to the common ancestor of a diverse modern group than to the ancestor of any other group, but is not itself part of the first group.

Liu et al. confirm through phylogenetic analysis that Diania cactiformis is closely related to the ancestor of modern arthropods, but not descended from that common ancestor. It has arthopod-like “sclerotinized” limbs (sclerotin is a protein found in the hard arthropod cuticle), and arthopod-like jointed limbs. Here’s a reconstruction:

Liu et al.’s analysis also shows that the fossil and other lobopods are “paraphyletic”: that is, some members of the “lobopod” group are more closely related to other non-lobopod taxa than they are to other lobopods. That makes the Lobopodia a false grouping, since it does not include all the descendants of one common ancestor. The authors conclude:

Irrespective of its exact position, Diania, with its stout and spiny limbs attached to a slender, vermiform body, remains a highly unusual creature. It is hard to envisage it as the progenitor of any modern arthropod group, yet it may derive from a grade of lobopodian that acquired a key evolutionary innovation—and the name-giving character for Arthropoda—whereby sclerotized, jointed appendages began to fully develop.

The second beast is a fossil cricket Schizodactylus groeningae, whose description was published by Sam Heads and Léa Leuzingers in a fairly obscure journal, ZooKeys (reference below, access free). The description was based on two specimens from the remarkable Crato Formation of Brazil, dating back about 112 million years. The formation is amazing because it preserved many delicate creatures, especially insects. You can see the veins of their wings, and sometimes even their colors! Here are a couple of non-crickets from Crato.

First, an Ephemeropteran (mayfly). Remember, this insect lived more than a hundred million years ago:

A grasshopper-like insect placed in the family Eincanidae:

Here’s the fossil cricket described by Heads and Leuzinger. It was formerly named Brauckmannia groeningae:

Notice the coiled wings and the “lateral processes” on the feet. These are similar to those of living “splay-footed crickets” that are placed in the genus Schizodactylus. And that’s the excuse for posting the fossil, for I didn’t know of these crickets, and they’re weird. Crickets in the family Schizodactylidae live largely in the sand dunes of Asia and Africa. Their splayed feet act, in fact, like snowshoes, helping them make their way over unstable sand. Here’s a modern one, Schizodactylus inexpectatus (photo copyright by Jan Sevcik):

The authors conclude that the fossil cricket shares so many features with the modern ones in this genus, including coiled wings and those “sandshoes,” that it should be placed in the genus Schizodactylus as well; and they renamed the fossil beast Schizodactylus groeningae. When a species is renamed (“synonymized”) in this way, that means that the earlier genus name, Brauckmannia, can never be used again.

27 Comments

Question – if the ancient cricket is placed in the same genus as the modern one that lives in desert locations, & the same rock formations where the ancient Schizodactylus was found contain mayflies, were they contemporary? Mayflies mean reasonably slow flowing water, & yet the crickets suggest sand or dunes?

How wide of a time span does the cricket & mayfly fossil deposit cover?
I expect relatively wet periods, with lots of rivers suitable for mayflies, could alternate with relatively dry periods, with lots of dunes suitable for weird crickets, over a time frame of thousands to tens of thousands of years.

Those crickets are weird, and it looks like Dr. Coyne was not the first person to be struck by their oddness – I like the species name of the living example “inexpectatus“.

Love it ! Looks like a construction toy so I shall dub the ‘walking cactus’ Diania legoformis

I understand that modern aquatic arthropods breathe using gills borne on appendages or body segments
Did early aquatic arthropods breathe using the same ‘technology’ ?

From what Jerry writes above: The Diania cactiformis is believed to be a close relative to the ancestor of modern arthropods (but not descended from that common ancestor)
Did this animal have gills ?
If so, where are they in the reconstruction illustration ?
More generally did all multicellular aquatic animals from this era use gills or are there other ways of extracting oxygen from water ?

Why is the sclerotin on the limbs shaped into bumps ? Perhaps to imitate aquatic vegetation ? Increased armour ?

OK ~ I’ve spent a few hours reading a little about the fascinating, confusing, mysterious early Cambrian & I’m going to make a complete guess & wait to get shot down…

I would appreciate comments from anyone who knows some biology ~ I do not

This is an aquatic, armoured, worm with pods & it’s a type of lobopod. It has a ‘nozzle’ on the front & it ‘vacuums’ up the debris from the sea bottom & processes it through its simple straight gut. The pods do not APPEAR to be differentiated in the Swiss-army-knife-fashion of the later arthropods & so I’m assuming that there might be attachments to the pods that have not fossilised.

I’m guessing that it had gill fronds where the pods join the tube body because diffusion would not permit sufficient oxygen throughput to fuel locomotion. Also movement would increase the amount of waste products ~ this creature would need to excrete a large amount of toxic ammonia & it is too long to do this down the gut. I understand that in modern aquatic arthropods the gills are generally considered to be the main route of ammonia excretion.

I wonder what the four pairs of front pods were used for ? They don’t look like they were for grasping. Maybe to clear surface debris for the nozzle ?

Dr Coyne, isn’t the velvet worm supposed to be related not just to the common ancestor of Arthropoda and Crustacea, but also the common ancestor of those with Chordata? In other words, the great grandfather of humans and flies?

No!
First, crustaceans are arthropods. Second, onychophorans are very clearly ecdysozoan protostomes closely related to arthropods.
The common ancestor of humans and flies is the common ancestor of all deuterostomes and all protostomes, the “urbilaterian”. Whatever it was, it was nothing like a velvet worm.